Cane Toads

Air Date: Week of April 28, 2000

In his latest National Geographic Radio Expedition, NPR's Alex Chadwick reports on how the South American cane toad got to Australia, and why Australians want it to go away.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood. Ecosystems are hard things to balance. Consider the challenges faced by European settlers in Australia. A hundred and fifty years ago, they brought in rabbits. Without natural predators, there were soon rabbits everywhere. Fine, the settlers said. We'll bring in foxes to eat them. Trouble was, the foxes found indigenous species easier to catch than rabbits, and the rabbits continued to multiply. It's all part of the chain of unintended consequences. And if you think the Australians learned from their bunny explosion, think again. It was just a prelude to something even more vexing. NPR's Alex Chadwick tells us why in his latest National Geographic Radio Expedition.

MAN: This ferry is going upstream, all stops to the university.

CHADWICK: Brisbane, halfway along Australia's east coast. At evening, a ferry churning up the Brisbane River to the last stop, the University of Queensland. Where we meet amphibian researcher Conrad Hoskin, and begin to look for something called a cane toad.

(Animal calls)

HOSKIN: The biggest ones I've seen have been up to about 24 centimeters.

CHADWICK: The toad search is a five-minute walk across campus to a small pond. It's gotten dark; huge bats skitter low overhead. Now, listen for the toads.

(Toad calls)

HOSKIN: There we go. And that's their call, going in the background there, that -- (Purrs).

(Calls continue)

CHADWICK: There are famously strange creatures native in Australia. The South American cane toad is not one of them. Farmers in the northeastern state of Queensland got some 60 years ago. The toads were supposed to eat sugar cane beetles. It turns out they don't. Mostly what they do is make more toads.

HOSKIN: The most amazing thing is, when they all metamorphose, they come out in waves. So, if she goes down and dumps, say, 25,000 eggs in, in one go, they'll all come out within about a month.

CHADWICK: Twenty-five thousand --

HOSKIN: Tiny little toads, yeah.

CHADWICK: In the decades after the thirties, cane toads spread quickly. And people began to discover one more very important cane toad factor. They're highly poisonous.

HOSKIN: It really is incredibly toxic, like it can kill dogs, cats. So it has no trouble killing wildlife that eat it. And the big problem is, a lot of the wildlife doesn't have the capacity to learn about the toads, and you know, they just don't get the chance to learn about them before it's too late.

(Animal calls)

CHADWICK: There are a lot of frogs in Australia, and a lot of creatures evolved to eat them, not expecting ever to encounter a poison toad. Where the cane toads appear, there are massive die-offs of Australian wildlife.

(Footfalls)

CHADWICK: Conrad had a long pole with a large net at one end, and we set off walking the edge of the pond, looking for toads.

(To Hoskin) So that's one?

HOSKIN: Yeah.

CHADWICK: Palm-sized, brown and warty on the back, pale yellow on the belly. The captured toad was utterly calm.

(To Hoskin) How dangerous is the toad to pick up, or handle, or be around, for us?

HOSKIN: It's not too bad. I've picked up thousands of toads, and I've never had any trouble.

CHADWICK: Well, you're handling them with bare hands, though.

HOSKIN: Yeah, that's fine. People lick these.

CHADWICK: They do?

HOSKIN: They've sort of got a hallucinogenic effect.

CHADWICK: Have you ever licked one?

HOSKIN: No. I'm not sure how many licks you can get away with. (Laughs)

CHADWICK: If you ate one of these toads --

HOSKIN: If I ate one, I'd die. I'm sure.

(Footfalls amidst toad calls)

CHADWICK: Already, cane toads have spread through almost half of northern Australia. They're getting near Australia's Yellowstone, Kakadu National Park. A wonderland of forest and wildlife. And many people worry what the cane toad could do there.

(Animal calls)

CHADWICK: Kakadu is in the center of Australia's north coast. It's in a place called the Northern Territory. The capital city is Darwin, named for the man who developed the theory of evolution. And a scientist there is waiting for the cane toad with Darwin in mind.

CHADWICK: Many wild predators do die from cane toads, Dr. Freeland says. But so far, none is extinct. He ran an experiment with a big Australian lizard called a gowana.

FREELAND: Very impressive. They're carnivorous.

CHADWICK: He used Darwin gowana from a local farm that was raising them for lizard hide. These gowana had never seen a cane toad.

FREELAND: What happened was that the gowana would immediately, I mean immediately, leap on the toad, grab it, hold it for five minutes. Then release the cane toad, which hopped away. And 15 minutes later, the gowana died. And I'm talking about, you know, five foot or more long lizard is dead within 15 minutes. It's quite dramatic.

CHADWICK: When the toads infest new wild areas, two thirds of the gowana die from eating them within months. But others do survive, and their numbers slowly return to normal. Maybe they learn to avoid toads, Bill Freeland thought, and he put a baby cane toad in with a big gowana. And the lizard gobbled the tiny amphibian like a jellybean gone bad -- ugh.

FREELAND: It went into a coma, and the lizard was in a coma for approximately six hours, with massive heart palpitations.

CHADWICK: That lizard, Dr. Freeland observed, had a very memorable lesson about cane toads. So, when it was fully recovered, he tried it with an adult toad.

FREELAND: And the first thing the gowana did was leap upon it, and attack the toad, and rolled over dead in 15 minutes. And it seems to me, at least, that the poor old gowana isn't too bright when it comes to learning about what it should and shouldn't eat.

CHADWICK: If the lizards don't learn, then something else is going on. Because when Dr. Freeland used wild gowana captured from areas where the toads are living, the results were very different.

FREELAND: None of them would even go near a cane toad. They just ignored them. And what seems to be going on, I think, is it's an evolutionary phenomenon. All we get that's happening here in Australia is that demand for the lizards are simply evolving to live with the cane toad. It's Darwinian selection before our very eyes, and it's really, really very, very exciting.

CHADWICK: His theory, here it is. A genetic difference among gowanas. Some eat cane toads. Some don't. The no-toad gowanas, and other creatures, too, that avoid them, will survive. And things will look pretty much the same, at least for a while.

(Toad and other calls)

CHADWICK: Dr. Freeland will tell you that Australia's road to toad hell is more likely a road to heck. Cane toads are a nuisance. Most wildlife probably will adapt. Which leaves people.

HOSKIN: Yeah, when I was younger, I used to really get into toad-busting, and knocking them over the fence with a golf club and the rest of it.

CHADWICK: University of Queensland zoologist Conrad Hoskin confesses his early cane toad interests, which many kids still pursue. It's hard to overstate just how much nuisance cane toads can be.

(Animal calls)

HOSKIN: There'd be maybe 40 toads, or just walking around suburban gardens in a place like Cairns. Just incredible, you know, you put the food out for the dog at night and they come up and eat the dog biscuits.

CHADWICK: Still, no creature is without its appeal. Conrad Hoskin, former toad warrior, now amphibian researcher. Fascinated by cane toads. And at least a little admiring.

HOSKIN: I don't find them ugly or anything. They're quite a -- you know -- maybe even an intelligent-looking little beast. And they just, they're so successful here despite everyone hating them, that you know, I really like them. But that doesn't mean I want them to stay.

CHADWICK: In Brisbane, Australia, for Radio Expeditions, this is Alex Chadwick, NPR News.

CURWOOD: Radio Expeditions is a co-production of NPR and the National Geographic Society. Our story on the cane toads of Australia was produced by Carolyn Jensen and recorded by Minoly Weathereau.

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